The present invention generally relates to cutting tools and, more particularly, to an apparatus and method for masking and coating cutting tools.
Many vehicle drivelines include power transmission devices having a number of gears in meshing engagement with one another. Each gear typically includes a plurality of teeth spaced apart from one another to properly mesh with the teeth of another gear. Each gear tooth must be precisely formed to provide reliable power transmission over an extended period of time.
The gears are constructed using gear cutting tools operable to remove material from a gear blank to define the gear teeth. In high volume manufacturing, it is desirable to quickly and accurately cut the gear teeth into a desired finished shape. It is also desirable to minimize the costs associated with constructing such gears. Accordingly, tooling design engineers strive to define manufacturing processes where not only the finished gear is constructed according to specification but where the cutting tools remain sharp for extended periods of time. A number of cutting tool manufacturers have constructed cutting tools from high speed steel, tungsten carbide and other cutting materials. In one instance, tool life has been extended by coating a tungsten carbide tool with a wear resistant material such as titanium aluminum nitride. Titanium nitride may be used as a coating for high speed steel applications. The coating is typically applied by immersing the tool in an environment containing a mixture of gas including titanium aluminum nitride or titanium nitride for six to eight hours. During exposure to the gas mixture, a coating is deposited on all surfaces exposed to this environment. Cutting tools exposed to this process have exhibited up to double the cutting life of similar tools not coated with the wear resistant material.
Once a cutting tool has become dull, it is common practice to grind the tip of the cutting tool to sharpen and/or redefine the cutting edge or edges. Unfortunately, the grinding process removes the coating previously applied to the cutting surfaces. Typically, the entire tool is exposed to the coating process once again to assure that the recently ground surfaces are coated. Because not all of the cutting tool is ground during the sharpening process, most of the cutting tool receives an additional coating thickness of the wear resistant material. It has been found that this grinding and recoating process may be repeated approximately five times until an undesirable result occurs. Specifically, once five or more layers of the coating are accumulated on the non-ground surfaces, the coating no longer properly adheres and causes the tool to fail.
It has been contemplated to remove the coating from the entire cutting tool prior to recoating using a chemical process. The chemical process negatively affects the cutting tool by removing the Cobalt from the cutting tool surface. The carbide microstructure is adversely altered and no longer exhibits the excellent cutting properties for which the tool is designed.
Alternately, it has been contemplated to machine more surfaces of the cutting tool to remove the previous coatings prior to reapplying another coating to the reground cutter. Unfortunately, the additional machining processes are very costly and may negatively interfere with the geometry of the cutting tool and repeatability of the machining operation. Accordingly, a need exists for a method of sharpening and recoating a cutting tool to extend the interval between cutting tool sharpening operations and to increase the number of times a given tool may be sharpened.
The present invention provides an apparatus and method of masking and coating a cutting tool. The method includes mounting a plurality of cutting tools in a holder, aligning a mask to cover a predetermined portion of each cutting tool, mounting the mask to one of the cutting tools and the holder, exposing uncovered portions of each cutting tool to an environment containing a depositable material and forming a coating on the uncovered portions of each cutting tool.
A fixture for mounting and masking cutting tools includes a tool holder and a mask. The tool holder has a cavity adapted to receive a plurality of cutting tools. The mask is coupled to the holder and aligned with the plurality of cutting tools where a majority of the surface area of each cutting tool is covered by the tool holder and the mask. The mask includes a shaped portion having a profile adapted to substantially match the profile of the shaped cutting tip for the cutting tool. The mask is positioned to expose a portion of the cutting tool to the surrounding atmosphere.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.